This invention relates to underreaming and chambering tools and more particularly to mechanisms in such tools for controlling the position of cutter arms.
Rotary drills are commonly used for earth boring operations. Such drills are employed in oil and gas wells as well as in mining operations. Often it is desirable to enlarge the diameter of a hole drilled in a downward direction starting at some point a substantial distance below the surface. In oil and gas wells this is commonly referred to as underreaming, whereas in mining it is commonly referred to as chambering. For ease of explanation, both operations are generally referred to herein as underreaming.
To effect underreaming operations a variety of underreamers, hole openers, and the like have been devised. With some devices the underreamer can only be installed on the drill string when underreaming operations are taking place. This requires removal of the drill string each time a change is made from straight drilling to underreaming of vice versa.
Other devices employ various controllable cutter actuators to move underreaming cutters into or out of underreaming position while a drill is connected below the underreamer for drilling purposes. Some such devices use fluid pressure, for example, due to recirculating drilling mud or the like to actuate a cutter into an extended cutting or underreaming position. In other known underreaming devices, mechanical adjustment of the drill string connected to the underreamer and fluid or pneumatic pressure applied through the drill string is used to move cutters to an underreaming position. One such device is disclosed in U.S. Pat. No. 3,817,339. In other devices purely mechanical control is employed.
Generally, presently known underreamers retract the cutter arms from an extended underreaming position to a retracted clearance position prior to the time that the underreamer is removed from the hole. If the underreaming arms do not retract before the underreamer is lifted from the hole, it is because there is a malfunction, or the arms have been wedged open by dirt or debris or other matter collecting under the cutter arms.
Particularly in mining operations, it has been found that following an underreaming operation, soil and rock debris tend to stick on the sides of the hole, thereby partially filling up the underreamed portion. This is undesirable and therefore it is desirable to remove the buildup of debris from the walls of the underreamed portion of the hole.